Substrate polishing and CO2 addition promote long growths of vertically aligned carbon nanotube carpets on aluminum foils by one-step CVD

Abstract

The one-step catalytic chemical vapor deposition (CCVD) meets the requirements for large-scale production of vertically aligned carbon nanotubes (VACNTs) to enable their numerous applications. Its main advantage at standard temperatures around 800 °C is the absence of growth saturation thanks to the renewal of catalytic particles through the continuous supply of a metal precursor. However, at lower temperature to grow VACNTs on substrates affording only medium range temperatures (eg. aluminum), some saturation occurs, especially as long syntheses duration are required due to the reduced growth rate. We show here how to overcome this limitation and produce tall and dense VACNT carpets at 615 °C on various grades of aluminum flexible foils. Adding CO₂ in the gas phase delays the saturation and avoid the degradation of the carpet for synthesis duration above 2 h. Results are consistently better on higher grade substrates, due to the impact of roughness on VACNT nucleation. The trade-off line between mass density and height often reported in the case of 2-steps CCVD does not affect the one-step process. On polished Al foils, VACNTs almost 1 mm-tall are obtained with densities greater than 100 mg/cm³. Growth rate and quality of VACNTs are at the state-of-the-art for syntheses at such moderate temperature.